Mr. Rutan designed the Spaceship to have a very low re-entry speed by making it have very high drag - the glider literally folds up to come down steeply and (relatively) slowly. Since they haven't gone to orbit, the speed can be low.
There is a minimum of ablative material as the heat build up is relatively low, at least in comparison to the Shuttle or 'normal' space capsules.
But what is equally impressive and can be seen in the photo of the interior, is the interesting artificial horizon.